U.S. patent number 9,382,927 [Application Number 13/698,952] was granted by the patent office on 2016-07-05 for apparatus and method for recuperation of hydraulic energy.
This patent grant is currently assigned to NATIONAL OILWELL VARCO NORWAY AS. The grantee listed for this patent is David Bengt Johan Ankargren, Jochen Pohl. Invention is credited to David Bengt Johan Ankargren, Jochen Pohl.
United States Patent |
9,382,927 |
Ankargren , et al. |
July 5, 2016 |
Apparatus and method for recuperation of hydraulic energy
Abstract
An apparatus for recuperation of hydraulic energy from an
actuator comprises a first hydraulic machine having a first drive
and a second hydraulic machine having a second drive mechanically
coupled to the first drive. The first hydraulic machine is in
hydraulic communication with an actuator, and the second hydraulic
machine (20) is in hydraulic communication with an accumulator.
Inventors: |
Ankargren; David Bengt Johan
(Kristiansand, NO), Pohl; Jochen (Gothenburg,
SE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Ankargren; David Bengt Johan
Pohl; Jochen |
Kristiansand
Gothenburg |
N/A
N/A |
NO
SE |
|
|
Assignee: |
NATIONAL OILWELL VARCO NORWAY
AS (Kristiansand, NO)
|
Family
ID: |
44991877 |
Appl.
No.: |
13/698,952 |
Filed: |
May 18, 2011 |
PCT
Filed: |
May 18, 2011 |
PCT No.: |
PCT/NO2011/000154 |
371(c)(1),(2),(4) Date: |
December 14, 2012 |
PCT
Pub. No.: |
WO2011/145947 |
PCT
Pub. Date: |
November 24, 2011 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20130199168 A1 |
Aug 8, 2013 |
|
Foreign Application Priority Data
|
|
|
|
|
May 20, 2010 [NO] |
|
|
20100738 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F15B
21/14 (20130101); B66C 13/02 (20130101); F15B
1/02 (20130101); F15B 2211/20546 (20130101); F15B
2211/761 (20130101); F15B 2211/20569 (20130101); F15B
2211/265 (20130101); F15B 2211/212 (20130101); F15B
2211/88 (20130101); F15B 2211/6336 (20130101); F15B
2211/625 (20130101) |
Current International
Class: |
F16D
31/02 (20060101); F15B 21/14 (20060101); B66C
13/02 (20060101); F15B 1/02 (20060101) |
Field of
Search: |
;60/414,421 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
100427771 |
|
Oct 2008 |
|
CN |
|
2113672 |
|
Nov 2009 |
|
EP |
|
11002212 |
|
Jan 1999 |
|
JP |
|
2004028212 |
|
Jan 2004 |
|
JP |
|
WO2009/119277 |
|
Oct 2009 |
|
JP |
|
Other References
US 3,693,039, 06/1976, Coeurderoy (withdrawn). cited by examiner
.
PCT/NO2011/000154 International Search Report Dated Aug. 16, 2011
(3 p.). cited by applicant .
PCT/NO2011/000154 Written Opinion Dated Aug. 16, 2011 (5 p.). cited
by applicant.
|
Primary Examiner: Wiehe; Nathaniel
Assistant Examiner: Nguyen; Dustin T
Attorney, Agent or Firm: Conley Rose, P.C.
Claims
The invention claimed is:
1. A method for recuperation of hydraulic energy from an actuator
during load conditions wherein at least one hydraulic pump is
configured to supply hydraulic fluid to the actuator, the method
comprising: mechanically coupling a first hydraulic pump and a
second hydraulic pump for torque transmission therebetween;
positioning a first valve in an actuator pipe between the actuator
and the second hydraulic pump; actuating the first valve to divert
hydraulic fluid from the second hydraulic pump away from the
actuator when the actuator is supplying hydraulic fluid to the
first hydraulic pump; hydraulically connecting the second hydraulic
pump to an accumulator; hydraulically communicating a second valve
with the actuator and the accumulator; actuating a second valve to
an open position; and allowing fluid to flow both from the actuator
to the accumulator and from the accumulator to the actuator after
and as a result of actuating the second valve to the open
position.
2. The method of claim 1 wherein a first drive coupled to the first
hydraulic pump and a second drive coupled to the second hydraulic
pump are mechanically connected to an electric motor, and wherein
the first hydraulic pump is in hydraulic communication with the
actuator, the method further comprising: connecting a controller to
the first and second hydraulic pumps and the electric motor,
wherein the controller is configured to control the displacement of
the first hydraulic pump, the second hydraulic pump and the power
of the electric motor; supplying a value of a position of the load,
a pressure of the actuator and a pressure of the accumulator to the
controller; and calculating a displacement of the first hydraulic
pump, the second hydraulic pump and the power of the electric motor
based on the values of the position of the load, the pressure in
the actuator and the pressure in the accumulator.
3. The method of claim 1, further comprising: identifying a type of
cycle; executing a control loop comprising: estimating a
recuperation potential; reconfiguring the first and second
hydraulic pumps and electric motor power; and monitoring and
controlling a charge of the accumulator; and finishing the
cycle.
4. An apparatus for recuperation of hydraulic energy from an
actuator, the apparatus comprising: a first hydraulic machine
having a first drive; a second hydraulic machine having a second
drive coupled to the first drive; wherein the first hydraulic
machine is in hydraulic communication with the actuator and the
second hydraulic machine is in hydraulic communication with an
accumulator; a first valve in hydraulic communication with the
second hydraulic machine, the actuator and the accumulator, wherein
the first valve is configured to transition between a first
position with the second hydraulic machine in hydraulic
communication with the accumulator and a second position with the
second hydraulic machine in hydraulic communication with the
actuator; and a second valve in hydraulic communication with the
actuator and the accumulator, wherein the second valve is
configured to transition between an open and a closed position;
wherein when the second valve is in the open position, fluid flow
is free to flow both from the accumulator to the actuator and from
the actuator to the accumulator through the second valve; and
wherein the second valve is in direct communication with the
actuator and in direct communication with the accumulator.
5. The apparatus of claim 4, wherein, the first and second drives
are connected to an electric motor.
6. The apparatus of claim 5, further comprising: a controller
configured to receive information relating to a position of a load
and a hydraulic pressure in the accumulator, and configured to
control the displacement of the first and second hydraulic machines
and the power of the electric motor.
7. The apparatus of claim 4, further comprising: a third valve
hydraulically positioned between the first hydraulic machine or the
second hydraulic machine and a reservoir; wherein the third valve
is in hydraulic communication with the reservoir and is configured
to transition between a first position with the return flow between
the first or second hydraulic machine and the reservoir open and
hydraulic communication with the accumulator is closed, and a
second position with flow from the first or second hydraulic
machine diverted to the accumulator.
8. The apparatus of claim 4, wherein the first valve is disposed
along an accumulator line extending from the accumulator to the
second hydraulic machine; and wherein the second valve is disposed
along an actuator line extending from the accumulator line to the
actuator.
9. The apparatus of claim 8, wherein the actuator line is connected
to the accumulator line at a point between the first valve and the
accumulator.
10. The apparatus of claim 8, wherein when the first valve is in
the first position, fluid is free to flow from the second hydraulic
machine to the accumulator along the accumulator line and through
the first valve; and wherein when the first valve is in the second
position, fluid is free to flow from the second hydraulic machine,
through the first valve, to the actuator line and is prevented from
the flowing from the second hydraulic machine, through the first
valve, to the accumulator along the accumulator line.
11. The apparatus of claim 10, wherein when the first valve is in
the second position, fluid is free to flow from the second
hydraulic machine, through the first valve, to the actuator line at
a point between the second valve and the actuator.
12. An apparatus for recuperation of hydraulic energy from an
actuator, the apparatus comprising: a first hydraulic pump having a
first drive, wherein the first hydraulic pump is in fluid
communication with the actuator; a second hydraulic pump having a
second drive coupled to the first drive; an accumulator line
extending from the second hydraulic pump to an accumulator; a first
valve disposed along the accumulator line; an actuator line
extending from the accumulator line, at a point between the first
valve and the accumulator, to the actuator; and a second valve
disposed along the actuator line; wherein the first valve is
configured to transition between: a first position to allow fluid
to flow from the second hydraulic pump to the accumulator along the
accumulator line and through the first valve; and a second position
to allow fluid to flow from the second hydraulic pump through the
first valve to the actuator line at a point between the second
valve and the actuator.
13. The apparatus of claim 12, wherein the second valve is
configured to transition between an open position and a closed
position; wherein the second valve is in the closed position, fluid
is prevented from flowing from the accumulator along the
accumulator line to the actuator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a 35 U.S.C. .sctn.371 national stage
application of PCT/NO2011/000154 filed May 18, 2011, which claims
the benefit of Dutch Patent Application No. 20100738 filed May 20,
2010, both of which are incorporated herein by reference in their
entireties for all purposes.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND
1. Field of Invention
The invention relates generally to an apparatus for recuperation of
hydraulic energy. More particularly, the invention relates to an
apparatus for recuperation of hydraulic energy, typically from an
actuator, typically a hoist, where a first drive of a first
hydraulic machine and a second drive of a second hydraulic machine
are mechanically connected, and where the first hydraulic machine
is in hydraulic communication with an actuator. The invention also
relates to a method for operation of the apparatus.
2. Background of the Technology
Hydraulic hoisting systems are included in an array of equipment
such as offshore and land based drilling rigs, winches and
equipment. The hoisting systems are regarded as the backbone of a
rig in terms of handling a drill as well as controlling a drilling
process.
Several of these hoisting systems exhibit a cyclic load profile
where a load is repeatedly lifted and lowered. At least in some of
the prior art hoisting systems potential energy is dissipated as
heat during lowering of the load.
Such systems are characterized by a large variation in the
operational envelope in terms of hook load and lifting speed, as
well as duration of a particular operation. The hoisting system is
thus dimensioned in order to fulfill the maximum power requirements
given by a certain operation. Therefore, the hydraulic power unit
of a typical hoisting system consists of several hydraulic
machines.
It is known to recuperate at least some of such potential energy by
utilization of a hydraulic transformer. U.S. Pat. No. 3,627,451
discloses a hydraulic transfer unit for transferring hydraulic
power at the same pressures and in either direction between two
separate and isolated hydraulic control systems.
U.S. Pat. No. 7,249,457 discloses a hydraulic system that has
gravitational load energy recuperation by opening a recuperation
piloted valve with a pilot pressure supplied by a hydraulic pump so
as to drive a recuperation hydraulic motor with a source of fluid
pressurized by gravity from the load. The recuperation hydraulic
motor drives the mechanical drive train of a prime mover that
drives the pump that supplies the load, and other pumps that supply
other loads.
None of the prior art documents discloses an energy management
system for cyclic load profiles in order to estimate the energy
recuperation potential to a hoisting system where energy is stored
in an accumulator.
The purpose of the invention is to overcome or reduce at least one
of the disadvantages of the prior art.
BRIEF SUMMARY OF THE DISCLOSURE
The purpose is achieved according to the invention by the features
as disclosed in the description below and in the following patent
claims.
There is provided an apparatus for recuperation of hydraulic energy
from an actuator, typically a hoist, where a first drive of a first
hydraulic machine and a second drive of a second hydraulic machine
are mechanically connected, and where the first hydraulic machine
is in hydraulic communication with the actuator, wherein the second
hydraulic machine is in hydraulic communication with an
accumulator.
At least the first or second hydraulic machine is here typically a
machine that is designed to operate as a variable displacement pump
and motor, for example an over-centre type pump/motor. The term
"displacement" is taken to mean displacement per revolution of the
pump/motor.
The actuator may take the form of a hydraulic ram, a hydraulic
pump/motor or any other suitable hydraulic equipment capable of
lifting a load directly or via machine elements such as a gear, a
rope or a pulley.
The accumulator may be a gas/liquid type of accumulator where a
gas, typically nitrogen, is compressed by hydraulic fluid flowing
into a closed bottle. The accumulator may also be of another
commonly known art, for example a hydraulic ram acting against a
spring. As the pressure of the accumulator is charge dependent, the
accumulator pressure is utilized for indicating the actual charge
of the accumulator.
By regulating the displacement of the second hydraulic machine it
is possible to charge the accumulator at a higher pressure than the
pressure driving the first hydraulic machine during lowering of the
load.
The drives of the first and second hydraulic machines may be
connected to an electric motor. Although the motor is termed
"electric motor" mainly in order to differentiate this motor from
machines acting as hydraulic motors, the motor may take the form of
a prime mover such as one or more of an electric motor, a
combustion engine or a hydraulic motor that is driven by a separate
hydraulic circuit.
The electric machine that is connected to the two hydraulic
machines serves several purposes. The connection between the two
shafts of two hydraulic displacement machines is in the art called
a hydraulic transformer. Hydraulic transformer control is known to
exhibit difficulties, especially due to non-linearities in a
control loop and the machines comparably low inertia compared to
the systems pressure level. Here the electric machine adds inertia
which eases the control problem. However, the electric machine is
even used in order to supply additional power that is dissipated in
the hydro-mechanical conversion process, see FIG. 2.
The apparatus may include a first valve that is in hydraulic
communication with the second fluid machine, the actuator and the
accumulator. The first valve is operable between a first position
where the second fluid machine is connected to the accumulator, and
a second position where the second fluid machine is connected to
the actuator.
By operating the first valve to the second position the apparatus
may be operated in a conventional manner without recuperation.
The apparatus may further include a second valve that is in
hydraulic communication with the accumulator and the actuator, and
where the second valve is operable between an open and a closed
position.
By opening the second valve, pressurized hydraulic fluid from the
accumulator may flow directly between the accumulator and the
actuator, for example for boost usage during conventional
operation.
In an alternative embodiment the apparatus may include a third
valve that is hydraulically positioned between at least the first
hydraulic machine or the second hydraulic machine and the
reservoir. Normally there is one third valve for each hydraulic
machine. The function of the third valve is to direct the flow from
the hydraulic machines to the accumulator.
This function is particularly useful for accumulator charging from
lowering loads such as after system operation with boost
accumulator usage. The apparatus may include a controller that
receives information of at least the relative position of the load
and the hydraulic pressure in the accumulator, and based on this
information and input from a conventional control system, controls
the displacement of the first and second hydraulic machines as well
as the power of the electric motor. The controller may be part of
the control system that may receive information of the desired load
position from say, an operator or a heave compensation system.
The apparatus may be operated by use of a method for recuperation
of hydraulic energy from an actuator during part load conditions
where more than one hydraulic pump is designed to supply hydraulic
fluid to the actuator, wherein the method includes: joining at
least two pumps mechanically for torque transmission them between,
whereby one pump becomes a first hydraulic machine and an other
pump becomes a second hydraulic machine; arrange a first valve in
an actuator pipe between the actuator and the second hydraulic
machine; activate the first valve to divert hydraulic fluid from
the second hydraulic machine away from the actuator when the
actuator is supplying hydraulic fluid to the first hydraulic
machine.
The method for recuperation of hydraulic energy is suitable for use
on a hydraulic apparatus that may include a first drive of a first
hydraulic machine and a second drive of a second hydraulic machine
are mechanically connected and connected to an electric motor, and
where the first hydraulic machine is in hydraulic communication
with an actuator, wherein the method may include: connecting the
second hydraulic machine hydraulically to an accumulator;
connecting a controller that is designed to control the
displacement of the first hydraulic machine, the second hydraulic
machine and the motor power to said machines and motor; supplying
values of load position, actuator pressure and accumulator pressure
to the controller; and calculating the displacement of the first
hydraulic machine, the second hydraulic machine and the motor power
based on the values of the load position, actuator pressure and
accumulator pressure to the controller.
A controller for this purpose may be designed with the help of one
of several methods known to those skilled in the art of control
engineering. A principal open loop controller can be stated as
follows:
##EQU00001## where the D.sub.m;main and D.sub.m;rec denote the
maximum displacement of main machine and the machine intended for
energy recuperation respectively, .epsilon. denotes the
displacement ratio of the two machines and i.sub.m;main and
i.sub.m;rec the number of machines for the two separate purposes.
The parameter i.sub.p denotes the number of hydraulic cylinders and
A.sub.p their area, the variables P.sub.Load and P.sub.Ace denote
the load and accumulator pressures respectively. The variable
v.sub.req denotes the require piston speed, and n.sub.el the shaft
speed of the electric machine.
The method may further include: define or identify type of cycle;
enter a control loop: estimate recuperation potential; reconfigure
the first and second hydraulic machines and electric motor power;
monitor and control accumulator charge; finish cycle.
The step of a flow chart carried out by the controller during
operation may thus include a first step where the type of cycle is
defined or identified, a second step where the recuperation
potential is estimated. In a third step the hydraulic machines as
well as the electric motor are reconfigured accordingly to findings
in the second step. A fourth step includes monitoring and control
of the charge of the accumulator. The state of the accumulator
charge as defined in the fourth step may require a new estimation
of the recuperation potential in the second step. The cycle is
finished in a fifth step that is entered when the load has reached
a desired position.
Change in operational details may be applicable depending on local
conditions. The operation will include estimation of available
energy for recuperation and control of the second hydraulic machine
to recover a major part of available energy to the accumulator, as
well as estimation of available energy in the accumulator for use
and control of the second hydraulic machine to utilize the major
part.
The apparatus according to the invention is well suited for
emergency operation if the electric motor should fail or for
providing hydraulic power to other systems.
It is a major benefit of the proposed apparatus that only minor
redesign from today's design is necessary, and that no major
additional components are required.
It is assumed that the apparatus and method according to the
invention best relates to operating conditions significantly below
the maximum specification. During these conditions, the existing
components can be utilized in a different way, so that energy
recuperation can be made possible. In that manner, the recuperated
energy from a lowering load can be utilized for a subsequent
lifting, so that the installed power of the entire system can be
reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
Below, an example of a preferred apparatus and method is explained
under reference to the enclosed drawings, where:
FIG. 1 shows a principle sketch of a vessel having a crane that is
operated by a hydraulic apparatus according to prior art;
FIG. 2 shows the same as in FIG. 1, but with a hydraulic apparatus
according to the present invention;
FIG. 3 shows a diagram of the principal hydraulic and control
circuits of the apparatus;
FIG. 4 shows the diagram in FIG. 3, but in an alternative
embodiment with additional valves.
FIG. 5 illustrates the use of recuperated hydraulic energy from the
accumulator for lifting a load;
FIG. 6 illustrates the recuperation of potential energy into
hydraulic energy for storage in an accumulator; and
FIG. 7 shows a flow chart of the steps included in the method
according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
On the drawings the reference number 1 denotes a vessel that
includes a crane 2. A load 4 is suspended from the crane 2 and
lifted by an actuator 6.
According to prior art as shown in FIG. 1, the actuator 6 is
connected to a hydraulic apparatus 8 by a pipe 10. The apparatus 8
includes at least two variable hydraulic pumps 12 that are driven
by their own electric motor 14.
When lifting the load 4, all energy is delivered by one or more of
the electric motors 14. When lowering the load 2, the potential
energy is dissipated as heat.
In FIG. 2 the vessel 1 is equipped with a hydraulic apparatus 16
for recuperation of potential energy from the load 4.
The hydraulic apparatus 16, that is shown in more detailed in FIG.
3, includes a first hydraulic machine 18 and a second hydraulic
machine 20, both designed to operate as variable pumps/motors.
The first hydraulic machine 18 has a first drive 22 in the form of
a shaft that is connected to an electric motor 24. The electric
motor 24 is connected to the second hydraulic machine 20 via a
second drive 26 also in the form of a shaft. The first and second
drives 22, 26 are thus mechanically connected through the electric
motor 24.
Both hydraulic machines 18, 20 communicate with a reservoir 28 for
hydraulic fluid.
The first hydraulic machine 18 is connected to the plus-side of an
actuator 6 via an actuator pipe 30. The actuator 6, in the form of
a hydraulic ram, carries a load 4. When the first hydraulic machine
18 supplies hydraulic fluid via the actuator pipe 30 to the
actuator 6, the load 4 is lifted.
The second hydraulic machine 20 is connected to an accumulator 34
via an accumulator pipe 36. A first valve 38 is coupled to the
accumulator pipe 36 and to the actuator pipe 30. When activated,
the first valve 38 divert the hydraulic connection of the second
hydraulic machine 20 from the accumulator 34 and to the actuator 6
as it may be necessary to supply the actuator 6 with hydraulic
fluid from both hydraulic machines 18, 20 when the accumulator is
working close to its design load and speed.
A second valve 40, see FIG. 3, is connected between the actuator
pipe 30 and the accumulator pipe 36. When activated, the second
valve 40 allows flow of hydraulic fluid between the accumulator 34
and the actuator 6.
A controller 42 receives, via sensor cables 44, information of the
relative load position from a position sensor 46, accumulator
pressure from a first pressure sensor 48 and accumulator pressure
from a second pressure sensor 50.
The controller 42 is designed to control the first and second
hydraulic machines 18, 20 and the electric motor 24 via control
cables 52.
FIG. 7 shows a flow chart indicting steps carried out by the
controller 42 during operation. In step 60 the type of cycle is
defined or identified. In step 62 the recuperation potential is
estimated. The hydraulic machines 18, 20 as well as the electric
motor 24 are reconfigured accordingly in step 64. A step 66
includes monitoring and control of the charge of the accumulator
34. The charge of the accumulator 34 as defined in step 66 may
require a new estimation of the recuperation potential in step 62.
The cycle is finished in step 68 when the load 4 has reached a
desired position.
The steps 60 to 68 as shown in FIG. 7 may be implemented using
software code stored in a media readable by a computer system not
shown but included in the controller 42.
Somewhat simplified, the type of cycles experienced in step 60
include lifting, lowering and keeping the load stationary. The
actual type of cycle may be identified by an input signal to the
controller 42, or by an actual movement of the load 4.
When the actual cycle, as defined or identified in step 60, is set
to be lifting of the load 4, the displacement of the first
hydraulic machine 18 is governed by the required lifting speed. An
arrow in FIG. 5 indicates the energy flow for a lifting cycle.
In step 62 the possible contribution from energy stored in the
accumulator 34 is estimated based on information of the
accumulators 34 charge. By utilizing this information and the
required power in the first hydraulic machine 18, the displacement
of the second hydraulic machine 20, acting as a hydraulic motor, is
adjusted in step 64. If required, the electrical motor 24 is
controlled in step 64 to supply necessary power.
In step 66 the information of the accumulator 34 charge is
monitored. Information is returned to step 62. The feed back from
step 66 to step 62 implies that a control loop including the steps
62, 64 and 66 will run until step 68 is entered.
The cycle finishes in step 68 when the load 4 has reached an
intended position.
When the actual cycle, as defined or identified in step 60, is set
to be lowering of the load 4, the displacement of the first
hydraulic machine 18, acting as an hydraulic motor, is governed by
the required lowering speed. An arrow in FIG. 6 indicates the
energy flow for a lowering cycle.
In step 62, the recuperation potential is estimated based on the
available power from the first hydraulic machine 18 as well as on
the available energy storage capacity of the accumulator 34. In
step 64 the displacement of the second hydraulic machine 20, acting
as a hydraulic pump, is set. In the unlikely event that
insufficient storage capacity is available in the accumulator 34,
surplus energy may be dissipated as heat in an emergency valve that
is not shown.
As previously stated, the information of the accumulator 34 charge
is monitored in step 66. Information is returned to step 62. The
cycle finishes in step 68 when the load 4 has reached an intended
position.
If the cycle as defined or identified in step 60 is set to hold the
load 4 stationary, the displacement of first hydraulic machine 18
is regulated to compensate for any leaks, while power for this
operation is supplied from the accumulator 34 via the second
hydraulic machine 20 and/or the electric motor 24.
In an alternative embodiment, see FIG. 4, third valves 54 are
positioned between the first hydraulic machine 18, the second
hydraulic machine 20 and the reservoir. A return pipe 56 connects
the third valves 54 with the accumulator.
When not activated, the return pipe 56 is closed at the third
valves 54, while the return flow from the hydraulic machines 18, 20
to the reservoir 28 is open. When activated, the third valves 54
divert the return flow from the hydraulic machines 18, 20 through
the return pipe 56 to the accumulator 34.
As stated in the general part of the description, this function is
particularly useful for charging of the accumulator 34 from
lowering loads such as after boost accumulator usage.
* * * * *